Missile propulsion



Patented Oct. 2, 1962 3,056,255 MISSILE PROPULSION Alfred M. Thomsen, 265 Buckingham Way, Apt. 402, San Francisco, Calif. No Drawing. ll iied Nov. 28, 1958, Ser. No. 776,740 2 (llaims. (CL 6035.4)

This application is essentially a rsum of a long series of experiments with solid propellants, it being my contention that this field offers far more latitude in diverse combinations of fuel and oxidizers than is possible when only liquid materials are under consideration. Particularly, I wish to avoid the use of such combinations as liquid oxygen and hydrocarbons, and the various substitutions for same that constitute the liquid practice of today. I shall commence with a purely academic consideration of gas volume and temperature, compared with solid reactants. I shall then introduce the method I have used in producing a controlled combustion of these substances instead of a detonation which would follow any attempt to use a mixture. Finally, I shall describe an experimental apparatus with which I have explored the relative merits of such combinations.

It is, of course, axiomatic that in determining the thrust of such a burning composition we are concerned only with the well known laws of action and reaction. These, in turn, depend upon the mass and velocity of the issuing jet, being a function of both.

It is not my intention herein to go into any detail of the kinetics involved. All such facts are well known to any engineer, and obviously, I can add nothing thereto. I do believe, however, that in reaching, by test firings only, for the ultimate in power development there is a tendency to lose sight of some fundamental facts. Even in ordinary combustion practice we easily reach such a temperature that the laws of dissociation become of paramount importance. Not until a portion of the heat generated has been absorbed in doing work is it possible to have the reaction go to completion.

By comparison with missile practice we reach the inescapable conclusion that much of the energy stored in the propellants is liberated after the products of a most incomplete reaction have been ejected from the missile, hence lost to the actual purpose for which it was destined. The torrent of flame emitted from a missile is positive evidence of the fact that said jet consists largely of a mixture of oxygen and fuel kept from combining by said law of dissociation until radiation and other sources of heat loss shall permit the reaction to go to completion. Obviously, all such facts are Well known but in firing practice each increment of energy added through the use of exotic fuel gives additional thrust in spite of the fact that so much of the total energy is wasted.

In consideration of these facts I believe that better propulsion is effected by increasing the velocity and mass of the jet than by simply raising its temperature to a point where said temperature defeats itself. To effect such a departure solid fuels seem particularly desirable as well as a solid oxidant, and ammonia compounds are particularly suitable owing to low heats of formation and final gas volume.

In my experiments I have found ammonium perchlorate the most suitable oxidizer and cyanogen compounds the most desirable fuel, particularly when commingled with just the right amount of a powdered light metal to raise the combustion temperature to a point just short of the dissociation point of said products of combustion. By cyanogen compounds I refer to the combination of ammonium with cyanogen, whether in the form of the normal cyanide, or cyanate, or thio-cyanate, or even ferro-cyanide, or to mixtures of the same. By light metals I refer to aluminum and to any metal having a lower specific gravity than aluminum.

Inasmuch as a mixture of such components would not be stable upon ignition but would detonate, I pack the reacting substances into separate divisions within the missile allowing intermixture of volatilized material to take place within a combustion chamber which may be a cavity within the mass itself. It should be noted that while the metallic part of said fuel adds nothing to the volume of gas it does add its mass to the jet and thus increases the total thrust. Also it is to be noted that said metals do combine with the chlorine of the perchlorate and thus give rise to volatile metallic compounds that act as a true gas when considered as components of the final jet.

To illustrate a method of packing these components within a missile I will now describe my experimental apparatus. I take a piece of pipe, two inches in diameter and nine inches long, sealed at each end with a cap, one of such caps being pierced with a central aperture onefourth of an inch in diameter. Said perforated cap is removed for the purpose of filling the tube with composition.

Into the tube, closed at the lower end with its cap, is now poured suificient of ammonium perchlorate to fill about one-half inch. A layer of talic, about one-sixteenth of an inch, is then carefully added and the layer pressed down firmly. About another one-half inch layer of fuel composition, ammonium cyanide commingled with powdered magnesium to say 10%, is then added; more talc as before and pressed down. When the tube is about half full it is placed under a press and about 1000 lbs. per sq. in. is applied. After compacting in this manner filling is resumed until the tube is full. The perforated cap is now screwed on and an axial hole with a diameter of one-fourth inch is drilled through the entire mass. This is the ignition tube. It is filled with meal powder.

The tube is next placed on the firing stand, supported in an upright position between three vertical pegs but free to move. The lever of a dynamometer is then contacted with the top of the tube and the charge fired. The thrust is thus directly measured in pounds, allowance being made for the loss in weight due to combustion. While this apparatus seems, and is, very crude, it does give comparative results.

Manifestly, such a small scale test gives no direct answer to the complex combustion problem represented when mass effect is taken into consideration. Only large scale firing tests such as are continually going on in the missile field can produce optimum results. However, it may be mentioned that the jet issuing from this tube is flameless after the first gush of smoke from the meal powder, and perhaps, until the entire wall area of the central combustion chamber is active. It is obvious that this entire concept is devoted to the use of solid propellants.

Obviously, even the largest missile could be filled so that alternate layers, or bands, of fuel and oxidizer would fill the entire body, a multiplicity of firing tubes being provided, and 50 disposed that the velocity of combustion could be varied at will according to the sequence of such layers or to a variation in composition of same. However, I do not limit myself to such a combination. As long as the fuel is substantially a cyanide composition and as long as fuel and oxidizer are so disposed within the missile that they occupy separate compartments, communicating with a separate combustion chamber, I consider such an arrangement as within the limits of this disclosure.

I claim:

1. The method of propelling a missile by the interaction of ammonium salts contained therein which comprises; so placing layers of ammonium perchlorate, serving as the oxidizer, and layers of ammonium ferrocyanide, serving as the fuel, that they Will be separate and distinct from one another within the missile but communicating with one another by channels that serve as containers for the igniting composition prior to ignition, and as combustion chambers after said ignition for the layered oxidizer and fuel combination, the final combustion products issuing from said combustion chambers as the propelling jet of the missile after such ignition and such combustion, fuel and oxidizer being so proportional as to produce maximum thrusts in actual firing.

2. The method of propelling amissile through the ignition and combustion of ammonium salts contained therein set forth in claim 1, with the added step that said ammonium ferrocyanide be commingled with a light metal to increase its fuel value.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Chem. and Eng. News, May 27, 1957, pages 18-23. 

1. THE METHOD OF PROPELLING A MISSILE BY THE INTERACTION OF AMMONIUM SALTS CONTAINED THREIN WHICH COMPRISES; SO PLACING LAYERS OF AMMONIUM PERCHLORATE, SERVING AS THE OXIDIZER, AND LAYERS OF AMMONIUM FERROCYANIDE, SERVING AS THE FUEL, THAT THEY WILL BE SEPARATE AND DISTINCT FROM ONE ANOTHER WITHIN THE MISSIL E BUT COMMUNICATING WITH ONE ANOTHER BY CHANNELS THAT SERV AS CONTAINERS FOR THE IGNITING COMPOSITION PRIOR TO IGNITION, AND AS COMBUSTION CHAMBERS AFTER SAID IGNITION FOR THE LAYERED OXIDIZER AND FUEL COMBINATION, THE FINAL COMBUSTION PRODUCTS ISSUING FROM SAID COMBUSTION CHAMBERS AS THE PROPELLING JET OF THE MISSILE AFTER SUCH IGNITION AND SUCH COMBUSTION, FUEL AND OXIDIZER BEING SO PROPORTIONAL AS TO PRODUCE MAXIMUM THRUSTS IN ACTUAL FIRING. 